The invention relates to circular stretchers for dry tubular fabrics, which are situated in front and back of a ring-shaped die for water removal or wet finishing through vacuum extraction.
In this case, the stretched tubular fabrics are passed through a ring-shaped die that encompasses the tubular fabrics, and a liquid medium is extracted from the tubular fabrics by a stream of air or hot air, or a liquid medium is siphoned through the tubular fabrics.
Such a device with stretchers is described in DE PS 198 28 206.
In this solution, a circular stretcher with a spreader ring and guide rollers is arranged in the running direction of the tubular fabrics in front and back of a ring-shaped die. The spreader ring is located inside the tubular fabrics, and held completely free of attachment between the guide rollers positioned outside the tubular fabrics. The tubular fabrics are passed between the guide rollers and the spreader ring, and spread out in circular fashion based on the geometry of the spreader ring. In this way, the tubular fabrics are to be passed by the ring-shaped die pressed down smoothly and without any folds.
In another design described herein, the two spreader rings of the circular stretcher arranged in front and back of the ring-shaped die are connected by a tubular, annular insert, so that an annular gap comes about between the parison and the guide surfaces of the ring-shaped die through which the tubular fabrics are passed.
The objective of this is for the flowing medium to have to make its way through a significantly longer path within the tubular fabrics, thereby enhancing the effect of the vacuum extraction.
Threading the tubular fabrics through the ring-shaped die requires that the diameter of one of the spreader rings connected to each other by the tubular, annular insert be smaller than the inner diameter of the ring-shaped die.
Instead of the two spreader rings with the tubular, annular insert, use can also be made of a tubular, rigid spreader body with circular collars, which is carried by guide rollers with the collars in the running direction of the tubular fabrics in front and back of the slit die, so that a uniform annular gap again comes about between the spreader body and the guide surfaces of the ring-shaped die, through which the tubular fabrics are passed.
Threading in the tubular fabrics again requires that the diameter of at least one of the collars be smaller than the inner diameter of the ring-shaped die.
The ring-shaped die is here provided with annular ring-like guide surfaces axial to both sides of its die slit, against which the tubular fabrics should lie smoothly.
In addition, this solution provides that the guide surfaces be extended in a tubular fashion to one or both sides of the die slit of the ring-shaped die.
The ring-shaped die consists of a die ring body with expansion area and a die insert with a die slit running around the inner periphery.
The die insert is to be arranged in the die ring body, and be interchangeable for varying die inserts with an inner diameter corresponding to the respective body width of the tubular fabrics.
A sufficient vacuum extraction requires that the tubular fabrics lie smoothly against the die slit. However, this is only ensured in the solution described in DE PS 198 28 206 if the inner diameter of the ring-shaped die, the diameter of the spreader rings of the circular stretchers located in front and back of the ring-shaped die and the diameter of the tubular fabrics are identical, or at least the outer diameters of the spreader rings are greater than the inner diameter of the ring-shaped dies.
However, if the tubular fabrics are smaller in diameter than the spreader rings, the tubular fabrics are overstretched directly at the spreader rings. The tubular fabrics then return to their original size, and also do not come to lie sufficiently against the die slit.
If the diameter of one or both spreader rings is smaller than the inner diameter of the ring-shaped die, the tubular fabrics do not come to lie sufficiently against the die slit.
This means that solutions in which a spreader ring has a smaller diameter than the inner diameter of the ring-shaped die for reasons of technological expediency do not ensure the desired vacuum extraction.
In the described solution, die inserts tailored to each body width of the tubular fabrics are provided, with an inner diameter corresponding to the respective body width. However, the knowledge acquired from this makes it necessary to adapt not only the die inserts to the respective body width, but also the spreader rings.
This means that a large number of die inserts and spreader rings are required at body widths of 200 to 950 mm, for example, which must be replaced any time the body width changes.
Practice often necessitates a rapid change of body widths, which then always requires a lot of time for retrofitting.
Another problem involves the high frictional resistance between the guide rollers and spreader ring, which can result in material damage in the case of sensitive tubular fabrics.
To ensure a continuous processing of the tubular fabrics, individual piece lengths of the tubular fabrics are sewn together into an overall length with round seams, so that the round seams of the tubular fabrics can cause them to become jammed between the guide rollers and spreader ring.
The object of the invention is to improve a generic circular stretcher in such a way as to be able to vacuum extract dry tubular fabrics with a wide range of varying body widths without replacing the spreader rings of the circular stretcher, and with a single inner diameter of the ring-shaped dies, and also preclude material damages caused by excessive frictional resistance and avoid jamming at the round seams.
The object is achieved according to the invention with two generic circular stretchers arranged in the running direction of the tubular fabrics in front and back of a ring-shaped die, and with a spreader ring held completely free of attachment inside the tubular fabrics, which stretch the tubular fabrics in a circular fashion. According to the invention, the spreader ring consists of individual roller carriers offset on the inner periphery of the tubular fabrics, which are interconnected in a star pattern, and whose outer ends each have two stretching rollers spaced apart from each other, which are used to stretch out the tubular fabrics and the stretching rollers along with the tubular fabrics passed over them abut outer rollers, which are mounted between the stretching rollers.
In this way, the spreader rings with their stretching rollers are held completely free of attachment within the tubular fabrics.
To reduce the frictional resistance and largely avoid tensile stresses in the tubular fabrics, the outer rollers preferably have a drive.
The tubular fabrics passed through the stretching rollers and outer rollers are stretched out in a geometry predetermined by the star-shaped layout of the stretching rollers.
In order to make a shape adapted to the ring-shaped die, a centering ring locked to the roller carriers of the circular stretchers is positioned directly in front and back of this die, and has an outer diameter equal to or greater than the inner diameter of the ring-shaped die.
The centering ring preferably is shaped the same as the ring-shaped die. This ensures that the tubular fabrics will be transported on the die slit of the ring-shaped die stretched out smoothly and without folds.
The roller carriers of the spreader rings are adjustable radially toward the tubular fabrics, so that the stretching rollers always come to lie against the driven outer rollers with the stretched tubular fabrics.
The interaction between the stretching rollers and driven outer rollers thereby yields a slip-free transport of the tubular fabrics.
The roller carriers are adjusted in a manner known in the art, either by hand, under a spring resistance, with pneumatics or through exposure to a magnetic force.
An adjustable circular stretcher is known from DE OS 3929599. In this solution, the tubular fabrics are guided over outwardly swivelable supporting arms.
The circular stretcher described here has a completely different design. The circular stretcher is mounted inside the stretched tubular fabrics at its ends, which makes it unsuitable for solving the above task for this reason alone. This is accompanied by tensile stresses in the tubular fabrics and a higher frictional resistance that arise in this solution, and are to be avoided with the new solution.
In another embodiment of the new solution, a conveyor belt also runs over the stretching rollers of each roller carrier to further reduce the transportation forces acting on the tubular fabrics.
The diameter of the tubular fabrics is preferably smaller than the centering rings, so that the tubular fabrics are overstretched directly in front and back of the ring-shaped die.
This overstretching of the tubular fabrics established the precondition for the tubular fabrics to come to lie against the ring-shaped die over a wide range of body widths. In this case, a total overstretching of the tubular fabrics of up to approx. 75% is here possible without any damage. The maximal permissible overstretching UD determines which body widths (tubular fabric diameter) DSW can be used with a ring-shaped die diameter DDxe2x88x92xc3x9cD=DD/DSW.
The tubular fabrics are advantageously overstretched not just starting at the centering rings, but already by the spreader rings, whose diameter is progressively adjustable. As a result, the frictional resistance at the centering rings is minimized.
In another embodiment, a stretcher device is locked to the spreader ring in front of it in the running direction of the tubular fabrics, and has a smaller diameter than that of the spreader rings. The stretcher device can be circular, spherical or hemispherical, or conical, etc.
Situating the stretcher device in front of the spreader ring brings about an incremental overstretching of the tubular fabrics, which further improves the stretching effect.
The solution according to the invention can be used to vacuum extract varying body widths within a wide range without replacing the spreader rings of the circular stretcher, and with a single inner diameter of the ring-shaped die. Material damage owing to an excessive frictional resistance and jamming at the round seams is precluded.
The invention will be described in greater detail below based on an embodiment.